Study on the Jet Evolution Mechanism and Prediction Model of the Dimensionless Limiting Jet Length for Pneumatic Drop-on-Demand Metal Droplet

Single metal droplets are widely used in electronic packaging and flexible circuit printing. However, the high density and interfacial tension of liquid metals make it difficult for the jet to stably generate single metal droplets, which greatly restricts the development of pneumatic drop on demand metal droplet ejection technology. In this paper, through experiments and numerical simulations, the jet motion states and internal fluid flow transition mechanisms during metal droplet generation are systematically investigated, and a dimensionless limiting jet length prediction model for stable single metal droplet generation is established. The results show that the dynamic competition and dominance transition between inertial force and interfacial capillary force fundamentally determine the jet motion states and internal fluid transition mechanisms. The pulse width is responsible for “activating” and “sustaining” the jet behavior, while the limiting jet length is primarily governed by the velocity provided by the supply pressure. The predictions of the dimensionless limiting jet length model are consistent with the experimental results, indicating that the model can effectively predict the limiting jet length for generating single metal droplets. The findings of this study are of significant importance for revealing the evolution mechanism of the jet during pneumatic drop on demand metal droplet generation and for achieving stable generation of single metal droplets, providing a theoretical basis for the further development of pneumatic drop on demand metal droplet additive manufacturing technology.